A photolithography has been known where a resist pattern is formed on a substrate in fabricating semiconductor devices or LCD substrates. The photolithography includes a series of processes including applying a resist to a semiconductor wafer (“wafer” hereinafter) to form a resist film on the wafer, and developing the wafer after exposing the wafer formed with the resist film to a light using a photomask, thereby obtaining a desired pattern.
These processes are generally performed using a resist application/development apparatus connected with an exposure apparatus. The resist application/development apparatus includes a carrier block where a carrier, called FOUP that houses a plurality of wafers, is introduced, and a processing block that includes processing mechanisms each performs a resist application process and a developing process. The carrier block includes a load-port equipped with a carrier-placement unit to place the carrier.
When the carrier is transferred to the load-port, wafers inside the carrier is transferred to a carry-in module to carry in the wafers into the processing block by a transfer mechanism such as, for example, a transfer arm installed in the carrier block. The wafers transferred to the carry-in module is brought into the processing block by a transfer arm installed in the processing block where a resist is applied to each wafer. After the resist is applied, the wafers are transferred to an exposure apparatus for an exposure treatment of the wafers. The wafers are then returned to the processing block by a transfer mechanism for a development process. Subsequently, the wafers are transferred from the processing block to the carry-out module for a transfer to the carrier block by the transfer mechanism, and returned from the carry-out module to the carrier by, for example, the transfer arm. Herein, the term “module” is used to indicate where the wafers are transferred.
As described above, when the carrier is placed in the carrier-placement unit of the load-port while the wafers are carried into and out of the carrier, a next carrier may not be transferred to the carrier-placement unit. As a result, the wafers may not be positioned appropriately on the processing module of the processing block and the exposure apparatus, that would have been processed otherwise, thereby reducing the work processing amount.
In view of the above, a stocker has been considered equipped with a retreat-area where the carrier is retreated temporarily. In this instance, after the wafers are unloaded from a first carrier (a starting carrier) transferred to the carrier-placement unit of the carrier-port, the first carrier is retreated to the retreat-area, and a second carrier (a secondary carrier) is placed in the carrier-placement unit to unload the wafers. Subsequently, after the wafers are unloaded from the second carrier, the second carrier is retreated to the retreat-area, and the first carrier is placed back into the carrier-placement unit so that the wafers, transferred from the first carrier and processed at the processing block, are returned to the first carrier. As described above, the work processing amount is expected to be improved by transferring the carrier between the carrier-placement unit and the retreat-area, because of an increased number of wafers unloaded from the carrier to the processing block and improved operating rate of the processing block and the exposure apparatus.
However, in a system where the carrier is transferred between the carrier-placement unit and the stocker, there may be a chance when the carrier that can house specific wafers is not placed in the carrier-placement unit when the specific wafers are transferred to the carry-out module. Here, in the processing block, the wafer takes a sequential process by transferring through the later part of the processing block according to an order that each of the wafers is entered, because, for example, processing conditions such as a processing time and temperatures of the wafers may vary on each lot. Namely, the transfer of the wafers in the processing block is controlled in such a way that a wafer transferred to the processing block later does not bypass a wafer transferred to the processing block earlier.
As a result, when a wafer is being held at the carry-out module for a relatively long time, the transfer of another wafer from the processing block needs to be halted, and an enough improvement of the work processing amount may not be achieved. Accordingly, a carry-out buffer module that can house a plurality of wafers is devised so that the wafers in the carry-out module are transferred to the carry-out buffer module by a transfer arm of the carrier block, and, after staying at the carry-out buffer module for a predetermined of time, the wafers at the carry-out buffer module are returned to the carrier by the transfer arm.
When the carry-out buffer module is installed, for example, the wafers may be carried to the carrier after all of the wafers are transferred to the carry-out buffer module, according to the order that the wafers are transferred to the carry-out module, thereby making a transfer sequence similar to the transfer operation in the processing block where a wafer brought into the processing block later does not bypass a wafer brought into the processing block earlier. However, in this situation, the wafers may be transferred to the carry-out buffer module even when the carrier is placed in the carrier-placement unit so that the wafers do not need to be transferred to the carry-out buffer module, thereby unnecessarily increasing the number of transfer operations by the transfer arm. The transfer time of the wafers from the carry-out module to the carrier is longer when the wafers are transferred to the carrier via the carry-out buffer module, as compared to the transfer time where the wafers are transferred from the carry-out module to the carrier directly, because an extended time is required for transferring the wafers from the carry-out module to the carrier. Also, since the number of transfer operations is increased, there is concern that a sufficient improvement of the work processing amount may not be achieved.